Can I recognize the faces of people around the world?
I thought it might be a helpful place to start:
https://en.wikipedia.org/wiki/Google_Street_View_privacy_concerns
The wiki is well cited, so should lead to some useful tidbits.  They break it down by continent and country.
Seems like a parallel to what you're doing, although, if you're not making your data public, I doubt you'll be facing the same privacy issues.
Also relevant would be: https://en.wikipedia.org/wiki/Expectation_of_privacy

Examples of places where a person has a reasonable expectation of privacy are a person's residence or hotel room and public places which have been specifically provided by businesses or the public sector in order to ensure privacy, such as public restrooms...
In general, one cannot have a reasonable expectation of privacy in things held out to the public.

My understanding is that there is no expectation of privacy in public places where you'd be capturing the images.